In hydroprocessing units, hydrogen is recycled to multiple points in the hydroprocessing reactor. A portion of the hydrogen recycle flow goes with the feed at the reactor inlet after being heated to 300° C.-400° C. via heat exchange with the reactor effluent and heating typically through a fired heater to provide hydrogen for the reactions, and a heat sink to minimize the temperature increase in the reactor as the highly exothermic desulfurization, denitrification, saturation, and hydrocracking reactions generate heat. In most cases where the hydroprocessed feed is diesel range or heavier, the rest of the recycled hydrogen is added to points along the length of the reactor at temperatures typically less than 100° C. The addition points are between catalyst beds where the temperature has risen to levels that are undesirable due to increased catalyst deactivation rates, increased cracking to gas compounds, and increased possibility of runaway. The added hydrogen is at temperatures colder than the reactor stream by 200° C.-350° C. to cool the stream back down to an acceptable range. In many operating units, the throughput is actually limited by the amount of cooling available from these added hydrogen quench streams to keep the reactor temperatures in a safe range.
Moreover the conventional design compresses all the recycle hydrogen up to the pressure required to get the hydrogen through all the reactor feed heating equipment and the entire length of the reactor even though a large fraction of this hydrogen bypasses the heating section and sections of the reactor as it is used as quench thereby wasting the energy that was added to the recycle gas from the compressor across the quench hydrogen temperature control valves. Only compressing the reactor inlet hydrogen and quench hydrogen streams to the pressure that is required to save compressor power is typically not done in design because it adds unnecessary complication to the compressor, and the flows need to be changed during a catalyst cycle in any event because the catalyst deactivates and shifts the temperature increase to bed further into the reactor.
Therefore, there is a need for an improved hydroprocessing method.